Welding controller



Dem 1949 G. J. LEXA 2,491,413

WELDING CONTROLLER Filed July 25, 1946 Patented Dec. 13, 1949 WELDING CONTROLLER George J. Lexa', Wauwatosa, Wis., assignor to Cutler-Hammer, Inc, Milwaukee, Wis., a corporation of Delaware Application July 25, 1946, Serial No. 686,183

3 Claims.

The invention relates to the control of current impulses and while not limited thereto it is particularly applicable to the control of a single impulse of welding current passed through a workpiece which is to be welded. The invention is an improvement on the system disclosed and claimed in the copending application of Cox et al., Serial No. 653,269, filed March 9, 1946, and assigned to the same assignee as the present invention.

In the aforementioned application a welding cycle is initiated by a pilot switch which controls the energizing circuit of an electromagnetic relay. Upon response the relaycommutates electronic means which thereupon initiate current flow in the welding circuit durin a preselected fraction of a single positive half cycle of an alternating voltage. The conductivity of the electronic means can be so adjusted that conduction of welding current may start at any desired moment after voltage zero at the start of a positive half cycle, whereby the total amount of energy supplied to the work may be regulated.

The employment of an electromagnetic relay as an intermediary between the pilot switch and the electronic means for initiating welding current flow requires careful design and adjustment of said relay as slight variations in its speed of response or bouncing of said relay have undesired effects. Thus a. more stable control having the advantageous characteristics of the earlier control aforementioned is highly desirable, and the present invention has among its objects to afford such improved control.

More specifically an object of the invention is to provide improved means for controlling the supply from a Welding transformer of a single unidirectional current impulse upon closure of a pilot control device.

Another object is to provide means for highly accurate control of the amount of energy supplied to the welding current by a single welding impulse. 7

Another object is to provide a: controller" of the aforementioned type which is quick and reliable in its response. v

. Another object is to provide protection against undesired current flow heretofore experienced as the result of failure in performance of the parts of the system.

Other objects and; advantages will hereinafter appear.

The accompanying drawing is illustrative of a welding systemembodying the invention.

- Referring. to 'theidrawingr thaSyStem as tiescribed in this paragraph is like that of the copending application aforementioned. L, L are the bus bars of an alternating current supply circuit. The circuit supplies current to a Welding transformer l8, having a primary winding Hi and a secondary winding 10 The winding It! is connected to welding electrodes H which operate in the usual manner to weld parts clamped therebetwe'en. One terminal of the winding Mi is connected to the bus bar L while its second terminal is connected to the cathode l2 of a gaseous tube or ignitron I2. The tube 12 has an anode 12 which is connected to the bus bar L and has also an ignition electrode l2, which is connected to the cathode 13 of a gaseous electron tube or thyratron 13. The tube 13 has an anode 13, a shielding electrode 13 connected to a cathode H and a control electrode I? connected to the cathode 13* through a capacitor l4. Connected across the terminals of the primary winding 'lll is the primary winding' I5 of an auxiliary transformer [5 which is also provided with a secondary winding I5".

Energy for operating some of the control circuits of the system is supplied through a transformer [6 which has a primary winding it connected across lines L and L two center tapped secondary windings l6" and I6 and a third secondary winding Hi. The secondary windin 15 has its outside taps connected to the anodes [1 and I! of a fulljwave rectifier shown as tube H which tube also has a filamentary cathode ll heated in any suitable manner (not shown). The center tap of the winding [6 is connected to an auxiliary bus bar l'8. Interpos'ed between the cathode W and the bus bar I8 is an energizing winding l9 of relay l9 and in series therewith a voltage divider comprising three series connected resistors 20, 2'] and 22. The relay H! has normally open contacts l9 connected between the bus bar L and the anode 3 The cathode H is further connected through a current limiting resistor 23 to the common terminal of a capacitor 24 and a variable resistor 25 which together are connected across the winding I 6? to form therewith a phase shifting network. The center tap of the winding lt is connected to a point intermediate of the resistors 26 and 2!.

The phase of the potential of the cathode l3 with respect to the grid 13 is modified by the phase shifting network. This potential is in turn under the control of a gaseous tube or thyratron 26 having a cathode 26 an anode 26, a control electrode 26 connected through a capacitor 21 to the cathode 126 and a shielding electrode 26 directly connected to the cathode 26 The cathode 2t is connected to the common terminal of resistors 2| and 22. The control electrode 26 is also connected to one terminal of the transformer winding while the other terminal of said transformer winding is connected to the negative bus bar i8. The anode 26 is connected through resistors 28 and 23 to the common terminal of resistors 2I and 22 and through a resistor 30 to the control electrode I3.

The voltage impressed upon the control electrode I3 from the phase shifting network aforementioned is modified by a gaseous tube 3| which has an anode Sl connected through a pilot switch 32 to the common terminal of the rcsis tors 20 and EI. The cathode 3I of tube 3i is connected to the common terminal of the resistors 28 and 29, and control electrode 3| is connected through a current limiting resistor 33 to one terminal of the transformer winding IS", the other terminal of which is connected to the bus bar I8. The control electrode 3I is also connected through a Joy-pass capacitor 33 to the cathode 3?. The shielding electrode 3I is directly connected to cathode 3P vision (not shown) may be employed to prevent voltage being impressed on the various tubes upon energization of the system until the respective tube filaments are heated to the normal operating temperature. The main electrodes of The usual pro- 1 tube I2 are connected by a relatively high impedance 35.

The operation of the system is as follows: When the bus bars L L are energized and the rectifier tube I7 becomes conducting, direct current flows from winding I6 over the rectifier I'I, through coil Is resistors to 22, back to winding IS The relay I9 is thus energized and closes contacts I9 to connect anode I3 to bus bar L As long as the control switch 32 is open the control grid I3 of tube I3 has impressed upon it a unidirectional potential which is negative with respect to the cathode I 3 by an amount equal to the voltage drop in the resistor 2I. superposed on this unidirectional potential is an alternating potential derived from the phase shift circuit 24-25. The phase of said alternating potential with respect to the cathode-grid potential may be varied in a well known manner by adjustment of the resistor 25 so that the resultant potential of the control electrode ls passes the critical ignition value at a selected moment of the positive half waves of the potential between the main electrode of tube I3 to start current conduction therethrough. As long as the switch 32 is open, the unidirectional potential is always greater than the amplitude of said alternating potential so that the resultant grid potential prevents initiation of current flow through the tube I3. As initiation of current conduction by the tube I2 depends upon current flow to the ignition electrode I2 through tube I3 the tube l2 also is prevented from conductmg.

While the tube I2 is nonconducting, a small current flows from the line L through the high impedance 35, winding l5 and in parallel with the latter through winding!!! to L The current through winding Ill is sufiicient to elimi nate the residual magnetism from transformer I0 due to previous high intensity magnetization by a welding current impulse, but it is insufilcient to induce a substantial current in the winding III which might cause arcing at the electrodes I I upon closure of the welding ourrent circuit through the workpiece. The current through the winding I5 induces a voltage in the winding I5 This voltage raises the potential of the grid 26 with respect to the cathode 26'' However, the rise is so low as not to substantially aifect the unidirectional negative bias of the grid 26 with respect to the cathode 26 due to the voltage drop through the resistor 22. Hence tube 26 remains nonconductmg.

If now the pilot switch 32 is closed, a unidirectional voltage equal to the voltage drop in resistor 2I is impressed upon the main electrodes of tube 3.I. The grid 3| has impressed on it by the winding IS an alternating potential which is substantially degrees out of phase with the voltage between L and L As long as switch 32 is open, however, the anode circuit is open and tube 3| does not conduct current. Upon closure of switch 32, tube 3I becomes conducting at the beginning of the first negative half cycle of the voltage of the bus bars L L and it thereafter remains conducting until the switch 32 is again opened. As soon as tube 3I becomes conducting, the component of the negative D. C. voltage bias on the grid I39 of tube I3, which is due to the voltage drop in resistor 2 I, is reduced to a value equal to the anode-cathode drop in the tube 3|. This reduction of the unidirectional r negative bias of tube I3 permits initiation of conduction of said tube at a moment. which depends upon the adjustment of the phase shifting resistor 25. Hence at a given moment of the positive half cycle of the main voltage the resultant potential of the grid I3 reaches the ignition value and current flow between the main electrodes of said tube I3 is established. For the remainder of the respective half cycle current flow in the'tube I3 results in a flow of ignition current to the ignition electrode I 2 of tube I 2 which then conducts and causes welding energy to flow through the transformer winding w to supply welding current to the welding electrodes II'.

The limitation of welding energy supplied by the welding transformer ID to a single half cycle or fraction thereof subsequent to closure of the switch 32 is controlled by the tube 26 in the following manner: When tube 3| conducts current, the voltage drop in resistor 29 is impressed upon the main electrodes of tube 26, but the latter is nonconducting because its control electrode is negative with respect to its cathode, due to the voltage drop in resistor 22. The alternating voltage in the winding I5 is superposed upon this negative bias of the grid 26 of tube 26. However, with the tube I2 conducting, the voltage impressed upon the winding I5- is increased as the impedance 35 is substantially short circuited by the current flowing through the tube I2. This increased voltage increases the alternating bias on the grid 26 supplied by the transformer winding I5 so that the biasing potential of the grid 26 permits initiation of conduction of the tube 26 whereupon said tube continues to conduct. As soon as the tube 26 becomes conducting the negative bias on the grid I3 is increased due to the voltage. drop in the resistor 28 resulting from the current flow in tube 26. Hence on the succeeding positive half cycles the grid I3 of the tube I3 remains again sufliciently negative to prevent conduction of v the tube I3 and ignition of the tube I 2, so that no more welding energy can flow through the welding transformer In. As long as the tube it is conducting, the voltage drop through the resistor 25 remains vsuiflciently high to mains tain the :tube 25 conducting, which in turn prevents conduction in tubes [3 and. I2. Hence if it is desired to obtain another impulse of weld ing current it will be necessary to openthe switch 32 which renders the tube 3| nonconducting. The tube 26 is thereby also rendered noneonducting because now the potential between its main electrodes is substantially zero. The system thus is returned' to its initial condition and. a second welding cycle may be initiated,v as aforedescribed, by closure of the switch 32.

If the rectifying tube I! should fail or failure should occur in the resistors 20-, 2| and 22, or any part thereof should become grounded, the relay i9 would. become deenergized or its energization would be reduced, so that it opens its contacts, thus preventing energization of tube 13- and thereby preventing unwanted'current flow through the welding transformer.

I claim:

1. In an energy control system the combination with electronic means including a thyratron tube, an alternating current supply for the main electrodes of said tube, means subjecting a control electrodeof said tube to an alterating voltage bias out of phase with the voltage of said main electrodes and means subjecting such control electrode to a unidirectional voltage bias, the former bias being for initiation of discharge of said tube and the latter bias normally preponderating the former to block current flow through said tube, of a pilot switch, electronic means responsive tooperation of said pilot switch and upon response beingv effective to terminate preponderation of the aforementioned unidirectional voltage bias thereby to permit the aforementioned alternating voltage bias to initiate flow of a single unidirectional current pulse through said tube at a given moment. during a positive half cycle of the voltage to which its main electrodes are subjected, and means responsive to abnormal conditions of the source of said unidirectional bias to interrupt the alternating current supply to the main electrodes of said thyratron tube.

2. In an energy control system the combinat on with electronic means including a thyratron tube, an alternating current supply for the main electrodes of said tube, means subjecting a control electrode of said tube to an alternating voltage bias out of phase with the voltage Of said main electrodes and means subjecting such control electrode to a unidirectional voltage bias theformer bias being for initiation of discharge of said tube and the latter bias normally prep-onderating the former to block current flow through said tube, of a pilot switch, electronic means responsive to operation of said pilot switch and upon response being effective to terminate preponderation of the aforementioned unidirectional voltage bias thereby to permit the aforementioned alternating voltage bias to initiate flow of a single unidirectional current pulse through said tube at a given moment during a positive half cycle of the voltage to which its main electrodes are subjected, and means conditioned as an incident to the aforementioned action of said last named electronic means to initiate as a function of discharge of said thyratron tube re-esta-blishment and maintenance of preponderation oi said unidirectional voltage bias pending reoperation of said pilot switch for terminating said preponderation.

' 3'; In an energy control systemthecombination. with el-ectron-iemeansincluding athyratron tuber, an alternating current supply for the main el'ec trodes of said tube-r a unidirectional biasing source, means subjecting a control electrode of said tube to an alternating voltage bias out of withv the voltage. or said main electrodes and to a bias from said unidirectional source the former bias being for initiation of discharge of said tube. and the latter bias normally preponderating the former to block current flow through: said tube, of a pilot switch, electronic means responsive to operation of said pilot switch and upon response being effective to terminate preponderation: of the aforementioned unidirectionali bias thereby to permit the aforementioned alternating voltage biasto initiate flow of a single unidirectional" current: pulse through said tube at; a. given moment during a positive half cycle of the voltage to which its main electrodes are subjected, and an electromagnetic relay in circuit with the current supply to the main electrodes of said" tubeand responsive to abnormal conditions of said unidirectional source to interrupt said current supply to the main electrodes of said tube.

4. In an energy control system the combination with electronic means including a thyratron tube, an alternating current supply for the main electrodes of said tube, means to subject a control electrode of said tube to an alternating voltage bias out of phase with the voltage of said main electrodes and to a unidirectional voltage bias normally preponderating to block the current flow through said tube, of a pilot switch, a second ends. third thyratron, means responsive to opera- 'tion of said pilot switch to render said second thryratron conducting for terminating preponderation of the aforementioned unidirectional voltage biasthereby to render the aforementioned alternating voltage-bias 'eifective'to initiate current flow through said first thyratron tube at a given moment during the positive half cycle of the voltage to which its main electrodes are subjected, and means to initiate conduction of said third thyratron'in response to the discharge current of said first thyratron to re-establish and maintain preponderation or said unidirectional voltage bias, pending re-operation of said pilot switch for terminating said preponderation.

5. In an energy control system the combination with electronic means including a thyratron tube, an alternating current supply for the main electrodes of said tube, means to subject a control electrode of said tube to an alternating voltage :bias out of phase with the voltage of said main electrodes and to a unidirectional voltage bias normally ,preponderating to block the current flow through said tube, of a pilot switch, a second and a third thyratron, means responsive to operation of said =pilot switch to render said second thyratron conducting for terminating preponderation of the aforementioned unidirectional voltage bias thereby to render the aforementioned alternating voltage bias effective to initiate current flow through said first thyratron tube at a given moment during the positive half cycle of the voltage to which its main electrodes are subjected, and means to initiate conduction of said third thyratron in response to the discharge current of said first thyratron to neutralize the effect of conduction of said second thyratron upon said first thyratron and to re-establish and maintain preponderation of said unidirectional voltage bias, pending re-operation of said pilot switch for terminating said preponderation.

6. In a welding system the combination with an ignitron, an alternating current supply for the main electrodes of said ignitron, welding electrodes deriving welding energy from said supply as a function of discharge of said ignitron, an electron discharge tube in circuit with the ignitor of said ignitron and said alternating cur: rent supply, a unidirectional biasing source, means subjecting a control electrode of said tube to an alternating voltage bias out of phase with the voltage of said main electrodes and to a bias from said unidirectional source the former bias being for initiating discharge of said electron tube and the latter bias normally prepon-derating the former to block current flow through said tube, of a pilot switch, electronic means responsive to operation of said ipilot switch and upon responding being effective to terminate preponderation of the aforementioned unidirectional bias thereby to permit the aforementioned altern'ating voltage bias to initiate current flow through said tube for supplying ignition current to said ignitor and initiating discharge of said ignitron at a given moment during a positive half cycle of the voltage to which its main electrodes are subjected, and an electromagnetic relay in circuit with the current supply to the main electrodes of said tube and responsive to abnormal conditions of said unidirectional source to interrupt said current supply to the main electrodes of saidtube.

7. In a welding system the combination with an ignitron, an alternating current supply for the main electrodes of said ignitron, welding electrodes deriving welding energy from said supply as a function of discharge Of said ignitron an electron discharge tubein circuit with the ignitor of said ignitron and said alternating current supply, means subjecting a control electrode of said tube to an alternating Voltage bias out of phase with the voltage of said main electrodes and means subjecting the control electrode to a unidirectional voltage bias the former bias being for initiating discharge of said tube and the latter bias normally lpreponderating the former to block the current flow through said tube, of a pilot switch, a first and a second thyratron, means responsive to operation of said pilot switch to render said first thyratron conducting and said first thyratron when conducting being effective for terminating preponderation of the aforementioned unidirectional voltage bias thereby to permit the aforementioned alternating voltage bias to initiate current flow through said electron tube for supplying ignition current to said ignitor and initiating discharge of said ignitron at a given moment during the positive half cycle of the'voltag'e to which'its main elec'-' trodes are subjected, and means to initiate conduction of said second thyratron in response to the discharge current of said electron tube, said second thyratron being then efi'ective to re-establish and maintain preponderation of said unidirectional voltage bias, pending re-operation of said pilot switch for terminating said pre ponderation.

8. In a welding system the combination with an alternating current supply, an ignitron having its main electrodes in circuit with said supply, welding electrodes deriving welding energy from said supply as a function of discharge of said ignitron, a first thyratron having its main elec trodes in circuit with said supply and the ignitor of said ignitron, means subjecting'a control electrode of said thyratron to an alternating voltage bias out of phase with the voltage of its main electrodes and means subjecting the control electrode to a unidirectional voltage bias the former bias being for initiating discharge of said thyratron and the latter bias normally preponderating the former to block the current flow through said thyratron, of a pilot switch, a second and a third thyratron, means responsive to operation of said pi-lot switch to render said second thyratron conducting and said second thyratron when conducting being effective for terminating preponderation of the aforementioned unidirectional voltage bias thereb to permit the aforementioned alternating voltage bias to initiate current flow through said first thyratron at a given moment during the positive half cycle of the voltage to which its main electrodes are subjected, and means to initiate conduction of said third thyratron in response to the discharge current of said ignitron, said third thyratron being then effective to neutralize the effect of conduction of said second thyratron upon said first thyraton and to re-establish and maintain preponderation of said unidirectional voltage bias pending re-operation of said pilot switch for terminating said preponderation.

GEORGE J. LEXA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,158,885 Palmer May 16, 1939 2,166,309 Lord July 18, 1939 2,169,023 Dawson Aug. 8, 1939 2,259,331 Vedder Oct. 14, 1941 2,290,543 Dawson July 21, 1942 2,347,935 Collom May 2, 1944 

